Conventionally, air locks for the removal of solid material from a pneumatic air conveyor usually consist of a housing having an inlet communicating with the vacuum line and an outlet communicating with atmospheric pressure air, or other medium into which the vacuum-conveyed particulate material is to be discharged. A rotor is mounted in the housing for driven rotation about its axis, which generally is horizontal. A plurality of radially directed blades or vanes extend from the hub of the rotor towards but not into engagement with a pair of opposed rigid arcuate walls coaxially arranged with the rotational axis of the rotor and located between and connected to the inlet and the outlet. Between the radial extremities of the blades and the arcuate walls are located flexible replaceable sealer elements which sealingly engage the arcuate walls. The housing also includes enclosing end walls. Rotation of the blades within the arcuate walls allow material to be removed from the pneumatic transport system without air passing into the pneumatic transport system.
Prevention of ingress of air depends on the effectiveness of the seals at the radial extremities of the blades. While such seals are replaceable, they wear relatively rapidly and commence to leak, causing choking by the particulate material conveyed by the vacuum line. It is expensive and cumbersome to replace seals as soon as they commence to leak and leaks, therefore, are usually accepted until the leakage and choking become intolerable.